Under certain operating conditions, engines that have high compression ratios, or are boosted to increase specific output, may be prone to low speed pre-ignition combustion events. During pre-ignition, combustion of an air-fuel mixture in the cylinder is initiated before spark. The early combustion due to pre-ignition can cause very high in-cylinder pressures, and can result in combustion pressure waves similar to combustion knock, but with significantly larger intensity. Various strategies have been developed for the detection and mitigation of low speed pre-ignition (LSPI) in lower engine speed ranges, where the occurrence of pre-ignition tends to be higher. For example, pre-ignition may be detected and differentiated from knock using a knock sensor, and then mitigated using cylinder enrichment, load clipping, torque limiting, etc.
However, the inventors herein have recognized that pre-ignition can also occur at higher engine speeds, such as above 4000 rpm. Detection of pre-ignition in this range may be more difficult to due to presence of mechanical engine noise. If the high speed pre-ignition (HSPI) goes undetected, it can turn into “runaway pre-ignition” and potentially cause rapid engine degradation.
The inventors herein have identified approaches to at least partially address the above issue. In one example approach, high speed pre-ignition may be better detected and addressed by a method comprising: indicating pre-ignition based on each of an integrated knock sensor output in a knock window and an integrated knock sensor output in a pre-ignition window. In this way, engine degradation due to high speed pre-ignition can be identified and mitigated.
As one example, an engine system may include one or more knock sensors arranged in, at, or along an engine block or coupled to engine cylinders. Output from the knock sensor generated in one or more of a first and second crank angle timing window may be used to identify abnormal combustion, such as those due to knock and/or pre-ignition. As such, the first crank angle timing window may be a pre-ignition window and the second crank angle timing window may be a knock window, wherein the pre-ignition window occurs earlier (in the engine cycle) relative to the knock window.
Sensor output generated in the knock and pre-ignition windows may be processed (e.g., band pass filtered, rectified, and integrated) to determine respective output intensities. For example, output from the knock sensor may be integrated in each of the knock and pre-ignition windows to determine respective intensity of knock and pre-ignition. Further, output from the knock sensor generated in each knock window and pre-ignition window may be integrated over a plurality of engine cycles. Additionally, peak values within each of the knock and pre-ignition windows may be estimated for the plurality of engine cycles. High speed pre-ignition may be determined based upon the integrated output in each of the knock and pre-ignition windows over the plurality of engine cycles. For example, high speed pre-ignition may be indicated when an increase in the integrated sensor output in the knock window is followed by an increase in the integrated sensor output in the pre-ignition window. As another example, high speed pre-ignition may be confirmed based upon a decrease in peak values of knock sensor output in the knock window along with a concurrent increase in peak values of knock sensor output in the pre-ignition window over the plurality of engine cycles. Furthermore, upon determining the presence of high speed pre-ignition in a given cylinder, mitigating actions that are specific to high speed pre-ignition may be performed. For example, fuel injection into the affected cylinder may be temporarily suspended, and intake air flow adjustments may be used to reduce the engine load.
In this way, high speed pre-ignition may be detected and alleviated. The technical effect of monitoring a transition of abnormal combustion events from knock windows to pre-ignition windows over a plurality of engine cycles is that the presence of high speed pre-ignition may be detected more accurately, without the results being affected (e.g., corrupted) by mechanical engine noise. Further, an existing knock sensor may be used to identify high speed pre-ignition, and better distinguish it from low speed pre-ignition. As such, by identifying high speed pre-ignition reliably, and remedying the high speed pre-ignition promptly, durability of the engine may be extended and engine performance may be enhanced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.